外文翻譯--金剛石刀具機械研磨過程中材料的去除機理

外文翻譯： Material Removing Mechanism for Mechanical Lapping of Diamond Cutting Tools LI Zeng-qiang， ZONG Wen-jun， SUN Tao， DONG Shen （ Center for Precision Engineering， Harbin Institute of Technology， Harbin 150001， China） Abstract： The material removing mechanism for mechanical lapping of diamond cutting tools was illuminated at the atomistic scale. In lapping process， phase transformation of the lapping region was the main reason for the material removal. Thus a three-dimensional model of a specimen of the diamond monocrystal and rigid diamond grit was built with the aid ofthe molecular dynamics（ MD） simulation. The force between all of the atoms was calculated by the Tersoff potential. After that， lapping with a certain cutting depth of 1.5 lattice constants was simulated. By monitoring the positions of atoms within the model， the microstructure in the lapping region changes as diamond transformed from its diamond cubic structure to amorphous carbon were identified. The change of structure was accomplished by the flattening of the tetrahedron structure in diamond. This was verified by comparing the radial distribution functions of atoms in the lapping and un-lapping regions.Meanwhile， the debris produced in lapping experiment was analyzed by XRD（ X-ray diffraction） . The results show that the phase transformation happens indeed. Keywords ： diamond cutting tools ； mechanical lapping ； material removing mechanism； molecular dynamics simulation It is an important way to turn the optical surface with natural diamond cutting tools to obtain high accuracy. The processed work-pieces surface has lower surface roughness and residual stress， and smaller metamorphic region than those machined in usual ways. Diamond is the most important material to make cutting tools in the ultra-precision machining， for it is an ideal brittle solid with the greatest hardness and resistance to plastic deformation of any material and has very high dimensional homogeneity. The sharpening method of diamond cutting tools is the key technology to obtain sharp cutting radius， good surface quality and small geometric tolerance1. There are many sharpening methods such as lapping， ion beam sputtering，thermal chemistry polishing， plasma polishing， oxide etching and laser erosion， etc. The most common and effective method is lapping2. The mechanism of the material removal in lapping has a lot of statements such as the micro-cleavage theory3， the thermal abrasion theory4， electro-abrasion theory5 and theory of fracture taking place in the hard direction6， etc. However， these explanations are only satisfactory in the particular situation. The explanation accepted by most people is that the hybridized orbit of the carbon converts from sp3 to sp2 in lapping， as demonstrated by van Bouwelen7， Grillo8， Hird and Field9. As yet， few man has verified it at the atomistic level. The extremely powerful technique of molecular dynamics（ MD）simulation involves solving the classical many-body problem in contexts relating to the study of matter at the atomistic level. Since there is no alternative approach capable of handling this broad range of problems at the required level of detail， molecular dynamics methods have been proved indispensable in both pure and applied research， as demonstrated by Rapaport10. Molecular dynamics analysis is an effective method in studying indentation， adhesion， wear and friction，surface defects and nano-cutting at the atomistic scale. Nowadays， MD analysis has already been employed to investigate the AFM-based nanolithography process using an AFM tool11 and atomic surface modification in monocrystalline silicon12. Therefore， it is an efficient way to approach the mechanism of the material removal in lapping using molecular dynamics simulation. From all the above， this study will focus on the material removing mechanism in diamond mechanical lapping using three-dimensional MD simulation. And the microcosmic phenomena in mechanical lapping will be presented and discussed. 1 Methods 1.1 Simulation modeling At the beginning， the mechanical lapping process of diamond cutting tools is introduced. The scaife used was made from a grey cast iron and was medium “ striped”（ radial grooves to hold diamond grit） .It was prepared for use by applying a film of olive oil to the surface， before a few carats of graded diamond grits were rubbed evenly into it. With the scaife running at a high speed， a diamond cutting tool was lapped by applying a load. In this process， the diamond grit was fixed in the scaife. So， the process belongs to the fixed abrasive polishing category13. Therefore， a model of a specimen of the diamond monocrystal and rigid diamond grit was built， as shown in Fig.1. Fig.1 Molecular dynamics simulation model of mechanical lapping of diamond cutting tools The crystal lattice of the specimen and the grit belonged to the diamond cubic system. The lattice constant of this system was 0.356 67 nm， which was represented as a. The control volume of the specimen must be large enough to eliminate boundary effects.Taking this into consideration， an optimum control volume was chosen based on an iterative process of increasing the control volume size until further increases did not affect the displacements and velocities of the atoms due to lapping. An optimum size of 50a 15a 30a was obtained， consisting of 183,930 atoms. Moreover， the periodic boundary condition was used in the z-direction to reduce the effects of the simulation scale. The specimen included three kinds of atoms ，namely ： boundary atoms， thermostat atoms and Newtonian atoms.To restrict the rigid-body motion of the specimen， the boundary atoms in the left and bottom layers of the specimen that were fixed in space were used to contain the Newtonian atoms.Thermostat atoms were also used to ensure reasonable outward heat conduction away from the control volume.Thermostat atoms and the Newtonian atoms obey the Newtons second law.The top surface of the specimen was（ 100）surface， which was exposed to the grit.The spherical diamond grit had a radius of 8a， consisting of 17,116 atoms.And it slid on the specimen with the depth of h. Before carrying out the molecular dynamics simulation on the lapping of diamond， it is important to ensure that the chosen potential function gives a reliable result for the simulation. Tersoff potential was used in the present simulation to dictate the interaction among the diamond atoms in this simulation14. The parameters in Tersoff potential for carbon were as follows ： A=1,393.6 eV， B=347.6 eV，=34.879 nm.1， =22.119nm.1 ， =1.572,4 10.7 ， n=0.727,51 ，c=380,49 ， d=4.384， h=.0.570 58， R=0.18 nm， and S=0.21 nm. Positions and velocities of the atoms were determined by the Verlet method as demonstrated by Maekawa and Itoh15.To simulate lapping under room-temperature conditions， the diamond atoms were arranged in a perfectdiamond cubic structure with the lattice parameters equal to their equilibrium values at an ambient temperature of 293 K. The ambient temperature was maintained by scaling the velocities of the thermostat atoms at every special time step.In this simulation， the 0.5 fs was selected as the time step to obtain a high accuracy. This simulation was calculated by the Lammps software16， and visualized by the VMD software17. The velocity of the lapping was 100a with 1.5a in cutting depth and 40a in lapping length. Before the simulation， the specimen had been relaxed for 10 000 time steps in order to maintain the thermal balance. 1.2 Experiment The test apparatus of lapping experiment is shown in Fig.2.The abrasive used was diamond grit with an average radius of 0.1 m.They were coated on the scaife in a ring with a radius of 120 mm.The diamond cutting tool was fixed on the arm by a special fixture.Then， the tool was lapped with the scaife running at 3 000r/min(ca.38 m/s)，under a load of 5 N which was obtained by adjusting the place of the weight. The debris was collected after 30 min lapping.Thereafter， the XRD studies were carried out by SHIMADZU XRD-6000. Fig.2 Schematic diagram of the lapping apparatus 2 Results and discussions 2.1 Molecular dynamics analysis The 3D view and cross-section view of the simulation are shown in Fig.3. The crystal lattices near the diamond grit are distorted when the diamond grit cuts into the specimen.The region including these crystal lattices is half-ellipse in shape.The region is under the diamond grit and a bit left to the center o. And the major axis of the ellipse is in the same direction as the composition of forces. Furthermore， this region moves left as the diamond grit slides. As shown in Fig.4 ， A1+A2A3 ， where O1O2 represents the surface of the workpiece.It shows that the removal materials do not pole up on both sides of the groove completely.Some materials are removed and form chips. It is a cutting process. Whereas， the existing A1 and A2 show that ploughing also occurs.So this state is the cutting state accompanied by ploughing. Fig.3 Microstructure of specimen after the grit sliding Fig.4 Section of the grooves in the longitudinal direction There are three key points in lapping， as shown in Fig.5. Firstly，atoms near the diamond grit are forced to make some displacement from their initial position.The crystal lattices including these atoms distort a little.The boundary between the distorted lattices and the perfect lattices is along the diamond（ 111） surface（ the black lines）as shown in Fig.5（ a） .The displacements of the atoms become bigger and bigger along with the diamond grit sliding left.More and more atoms deviate from their initial position.The lattices including these atoms distort seriously.The phase transformation that the diamond cubic diamond transforms into amorphous graphite starts on a few atoms （ in the dark circles） at the end of this moment.That is to say that the hybridized orbit converts from sp3 to sp2. Secondly， the lattices below the diamond grit have the worst distortion and the boundary faceting along the（ 111） surface extend to the deeper layer， as shown in Fig.5（ b） . More atoms transform from diamond cubic diamond to amorphous graphite ， especially those in the dark circle. Besides，some atoms are taken away by the diamond grit.Thirdly， some lattices revert a little with the force minimizing， as shown in Fig.5（ c） . However，the atoms which have the phase transformation cannot revert to their initial phase， especially those in the dark circle. Therefore， the groove is to the left on the surface of the diamond specimen. Fig.5 Scattergrams of atoms in longitudinal section A in different states 2.2 Bond formation From the simulation， it is found that the phase transformation is due to the flattening of the tetrahedron structure in diamond cubic diamond， as shown in Fig.6.The position transformation at progressive time steps is demonstrated in Fig.7. Fig.6 Crystal cell of the diamond crystal lattice taken out from the circular region in Fig.5（ a） As shown in Fig.7（ a）， the tetrahedron is deformed when the grit slides close. And the deformation is serious when the grit cuts into section A， as shown in Fig.7（ b） . The tetrahedron is flattened a little.Soon after， the tetrahedron deforms badly， as shown in Fig.7（ c） .Its four vertexes are almost on a plane and some bonds are broken. At the same time the phase transformation is accomplished. Fig.7 Change of the tetrahedron marked in Fig.6 when the grit slides 2.3 Pair correlation function The pair correlation functions of the specimen and the chip are shown in Fig.8 and Fig.9 respectively.The curve in Fig.8 is syllabified to a lot of clear peaks， which are the same as the diamonds radial distribution fuction(RDF). However， there are only two peaks in Fig.9, and the peaks are continued, which illuminates that amorphous exists in debris atoms. Therefore， it is sure that the phase transformation takes place in lapping. Fig.8 Pair correlation function of specimen atoms Fig.9 Pair correlation function of debris atoms 2.4 XRD Fig.10 shows the X-ray diffraction（ XRD） analysis of the debris produced in the lapping experiment. It demonstrates that the amorphous carbon ， small diamond particles or chips and Fe-C compositions（ like Fe7C3 and Fe5C2） exist together in the debris. Consequently， the amorphous carbon is produced in lapping， which corresponds to the simulation result. Fig.10 XRD analysis of the debris produced in the experiment 3 Conclusions （ 1） A three-dimensional MD model about the atoms of diamond cutting tools and diamond grit is built by using the molecular dynamics. Lapping at a special cutting depth is simulated. （ 2） The boundary of the transformation zone is regular ， faceting along （ 111 ） surface. The microcleavage only occurs inside this boundary. （ 3） Interaction between the diamond grit and diamond specimen leads to a phase transformation event.An amorphous transformation appears as the grit slides.And it is expounded from the comparison between the bond formatting and pair correlation function. Moreover， it has also been proved in the lapping experiment. References： 1 Yuan Z J， Yao Y X， Zhou M， et al. Lapping of single crystal diamond tools J CIRP Annals-Manufacturing Technology， 2003， 52（ 1）： 285-288. 2 Uegami K ， Tamamura K ， Jang K K. Lapping and frictional properties of diamond， and characteristics of diamond cutting tool J Journal of Mechanical Working Technology， 1988， 17（ 8）： 147-155. 3 Tolkowsky M. Research on the Abrading， Grinding or Polishing of Diamond D London： City and Guilds College， University of London， 1920. 4 Bowden F P， Tabor D. Physical Properties of Diamond M Oxford： Clarendon Press， 1965. 5 Brezoczky B ， Seki H. 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VMD： Visual molecular dynamics J J Molec Graphics， 1996， 14： 33-38. 金剛石刀具機械研磨過程中材料的去除機理 李增強，宗文俊，孫 濤，董 申 （哈爾濱工業(yè)大學精密工程研究所，哈爾濱 150001） 摘要： 該材料，移除為的鉆石切割工具的機械研磨的機制被照亮在的原子論的的的的規(guī)模。在研磨過程中研磨區(qū)，相轉變材料去除的主要原因。因此，金剛石單晶和剛性金剛石磨粒的標本的三維模型的建立與援助的分子動力學（ MD）模擬。所有的原子之間的力量計算 Tersoff潛力。后認為，與一個 1.5晶格常數的的一定的的切削深度研磨進行了數值模擬。通過監(jiān)測模型內的原子的位置，在金剛石研磨地區(qū)的鉆石立方結構轉變?yōu)闊o定形碳的微觀結構進行了鑒定。完成在鉆石的四面體結構的扁平化結構的變化。這驗證了原子的徑向分布函數的研磨和聯合國研磨 regions.Meanwhile的，研磨試驗產生的碎片，通過 XRD（ X射線衍射）分析比較。的結果表明，的相位轉型會發(fā)生確實。 這是一個重要途徑，把光學表面與天然金剛石刀具獲得高的精度。處理工作件表面具有較低的表面粗糙度和殘余應力，小于常規(guī)方 法加工的變質地區(qū)。 鉆石是最重要的物質，在超精密加工的切削工具，它是一種理想的最大的硬度和耐磨性的任何材料的塑性變形的脆性固體，具有非常高的維同質。金剛石刀具刃磨方法的關鍵技術，獲得鋒利的切削半徑，良好的表面質量和幾何公差小1。有許多方法，如研磨，離子束濺射，熱化學拋光，等離子拋光，氧化腐蝕和激光侵蝕等銳化最常見和最有效的方法是研磨 2。在研磨材料去除機制有一個報表很多，如微切割理論 3，熱磨損理論 4，電磨損理論 5和斷裂理論的努力方向 6，等等。然而，這些解釋是只有在特殊情況令 人滿意。大多數人所接受的解釋是，從 SP3 雜化軌道的碳轉換到 SP2 作為由面包車 Bouwelen 證明，在研磨 7，格里洛 8，本手冊所有提及和現場 9。到目前為止，一些人已證實它在原子水平。 極其強大的技術分子動力學（ MD）模擬涉及解決有關的物質在原子水平的研究背景的經典多體問題。由于沒有替代方法能夠在所需水平的細節(jié)處理這個問題的廣泛，分子動力學方法已被證明是不可或缺的純粹與應用研究，由Rapaport 表明 10。分子動力學分析是一個有效的方法，在學習壓痕，附著力，耐磨損和摩擦，表面缺陷，并在 原子尺度的納米切割。如今，醫(yī)師分析已經被調查基于 AFM 的納米光刻過程中使用的原子力顯微鏡工具 11和硅原子在單晶硅表面改性 12。因此，它是一種有效的方式來處理的材料去除機制，研磨使用分子動力學模擬。 所有上述，本研究將集中在材料，消除金剛石機械研磨使用三維的 MD模擬的機制。和機械研磨的微觀現象，將介紹和討論。 1 研究方法 1.1 仿真建模 在開始時，介紹了金剛石刀具機械研磨過程。斯凱夫使用了從灰鑄鐵中的 “條紋 ”（徑向槽舉行金剛石磨粒）。 通過膜表面的橄欖油，之前幾克拉分級金剛石顆粒均勻揉入準 備使用。斯凱夫在高速運行，鉆石刀具研磨應用負載。在這個過程中，金剛石磨粒固定在斯凱夫。所以，這個過程屬于固定研磨拋光類 13。因此，始建金剛石單晶和剛性金剛石磨粒的標本模型，如圖 1 所示。 圖 7-1 關于金剛石切割工具機械研磨的分子動力學仿真模型 晶格的標本和砂礫屬于鉆石的立方系統。該系統的晶格常數為 0.356 67 納米，這是作為一個代表。試樣的控制量必須足夠大，消除邊界 effects.Taking 考慮到這一點的，被選為最佳控制量的基礎上增加控制音量大小，直到進一步增加并不影響原子的位移和速度的迭代過 程由于研磨。一個最佳規(guī)模為50A15A30A， 183930 原子組成的。此外，周期性的邊界條件是在 z 方向，以減少仿真規(guī)模的影響。標本包括原子 3種，即：邊界原子，恒溫原子和牛頓 atoms.To的限制的剛體運動的標本，在標本固定在空間的左側和底部層的邊界原子包含牛頓 atoms.Thermostat 原子也被用來確保合理向外熱傳導遠離控制 volume.Thermostat 原子和牛頓原子服從牛頓第二 law.The 排在前面的標本（ 100）表面，這是暴露球形金剛石磨粒 grit.The 了一個 8A 的半徑，它與深度 h 的標 本下滑 17,116 atoms.And 組成。 開展對金剛石研磨的分子動力學模擬之前，重要的是要確保所選擇的潛在功能提供了一個可靠的模擬結果。在目前的模擬 tersoff 潛力，決定在這個模擬 14鉆石的原子之間的相互作用。 Tersoff 碳勢參數如下： = 1,393.6 EV， = 347.6 EV，= 34.879 nm.1， = 22.119nm.1， = 1.572,410.7， N = 0.727,51， C = 380,49， D = 4.384， H = .0.570 58， r = 0.18 納米，和 S = 0.21 納米。位置和原子的速度 Verlet方法，確定由前川和伊藤表明 15為了模擬在室溫條件下研磨，鉆石的原子排列在 perfectdiamond 立方結構的晶格參數等于其均衡值 0.5 FS，通過擴大在每一個特殊的時間 step.In 這個模擬恒溫 原子的速度保持在 293 K 時的環(huán)境溫度環(huán)境溫度，被選定為時間步長，獲得了很高的精度。 這由 Lammps 軟件 16，模擬計算和可視化的 VMD 軟件 17。的研磨速度100A 1.5A 切割研磨長度的深度和 40A。前仿真，標本已放寬為 10 000 個時間步以保持熱平衡 。 1.2 實驗 研磨實驗測試儀器顯示帶有平均 0.1m.They的半徑在 Fig.2.The 磨料金剛石磨粒斯凱夫的 120 mm.The 鉆石刀具半徑涂在環(huán)固定于通過一個特殊的fixture.Then 的手臂， 斯凱夫運行在 3000r/min（ ca.38 米 /秒）， 5 這是通過調整重量地方獲得的列印負荷下，研磨工具。碎片收集 30 分鐘 lapping.Thereafter 后，進行了 X 射線衍射研究由島津 XRD-6000 型。 圖 7-2 研磨裝置示意圖 . 2 結果與討論 2.1 分子動力學分析 3D 視圖和截面模擬如圖 3 所示。當金剛石磨粒到 specimen.The 地區(qū)的削減，包括這些晶格是在 shape.The 地區(qū)的半橢圓形金剛石磨粒和中心 O 左位下，附近的金剛石磨粒的晶格扭曲。和橢圓的長軸是在同一方向的部隊組成。此外，該地區(qū)移動離開鉆石砂礫幻燈片。 如圖 4 所示， A1 - A2A3 的，其中 O1O2 表示的 workpiece.It 的的表面，去除材料不都槽 completely.Some 材料兩側被刪除和形式的芯片極了。這是一個切割過程。然而，現有的 A1 和 A2 顯示犁地也 occurs.So 這種狀態(tài)是春耕陪同的切削狀態(tài)。 圖 7-3 磨粒切削后的微觀結構 圖 7-4 凹槽的橫截面 如圖 5 所示，在切割過程中有三個關鍵點，首先，附近的金剛石磨粒原子被迫作出一些位移，從他們最初的 position.The 包括這些原子的晶格扭曲之間扭曲格和完美的晶格 little.The 邊界是沿著金剛石（ 111）表面（黑線）圖（一）所示。原子位移變得更大，隨著金剛石磨?；瑒?left.More 和更多的原子偏離他們的的初始 position.The 格，包括這些原子更大歪曲 seriously.The 階段轉變，金剛石立方金剛石轉變成非晶質石 墨開始在此 moment.That 年底說，從 SP3 雜化軌道轉換到 SP2 上幾個原子（黑眼圈）。其次，下面的金剛石磨粒的晶格有最壞的失真和小面沿（ 111）表面延伸到更深的層的邊界，在圖 5（ b）所示。更多的原子轉變從鉆石的立方金剛石的非晶質石墨，尤其是那些在黑暗中圈。此外，一些原子鉆石 grit.Thirdly，一些格與最小化的力量恢復了一點，在圖 5（ c）所示。然而，有相變的原子不能恢復到其初始階段，特別是那些在黑暗中圈。因此，凹槽是表面上的鉆石標本左。 圖 7-5 不同狀態(tài)下截面 A 中的原子分布圖 2.2 變形的形成 從這個模擬圖，我們可以發(fā)現立方金剛石的相變決定于其四面體結構的變形程度，如圖（ 6）所示。圖（ 7）展示了此變形隨時間的變化。 圖 7-6 圖 5 中環(huán)形區(qū)域內金剛石晶格的單晶體結構 圖 7 表明了當磨粒切削過后，四面體結構發(fā)生了變形。如圖 7（ b）所示，當磨粒切削到 A 截面時，將發(fā)生嚴重的變形。四面體結構稍微變得平坦。圖（ 7）c 所示，四面體馬上又發(fā)生了很嚴重的變形，導致它的四個頂點基本在同一平面上，甚至有些四面體結構被破壞了。此時，相變發(fā)生了。 圖 7-7 圖 6 中的結構在磨粒作用后其四面體的變形情況 2.3 一對相關函數 圖 8 和圖 9 各自列出了試樣和切屑的相關函數。圖 8 中的曲線與徑向分布函數（ RDF）一樣，由許多清晰的波峰組成。圖 9 卻只有兩個波峰，但波峰是連續(xù)的，它表明了碎屑原子里存有無定形結構。因此，我們可以確定，在切削過程中同時發(fā)生著相變。 圖 7-8 樣本原子的一個相關函數圖 圖 7-9 碎屑原子的一個相關函數圖 2.4 X 射線衍射 圖 10 表明了使用 X 射線衍射分析了研磨實驗中碎屑的產生過程。它表明碎屑中含有無定形碳、微小金剛石顆?；蛩槠约昂艰F（如2537 CFeCFe 和）。因此，無定形碳是在研磨的過程中產生的，這與模擬結果相符合。 圖 7-10 實驗中碎屑產生過程的 X 射線衍射分析 3 總結 （ 1） 通過分子動力學分析建立了一個關于金剛石刀具原子和金剛石磨粒的三維模型，在一個特定的深度進行模擬切削。 （ 2） 變形區(qū)的隨邊界沿表面（ 111）呈現出有規(guī)則的分布，邊界內部僅僅發(fā)生細微的分裂。 （ 3） 金剛石磨粒和樣本之間的相互作用導致了相變的產生，并隨著磨粒的移動發(fā)生了無定形變化?？梢酝ㄟ^對總體結構和一對相關函數的比較來分析這個過程。另外，也可以通過磨削實 驗進行論證。 參考文獻： 1 Yuan Z J， Yao Y X， Zhou M， et al. 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